In this three year project, we will define effects of commonly used anesthetic drugs on somatosensory cortical evoked potentials (SCEPs) so that effects of anesthetics on these responses can be separated from the effects of surgical manipulation of the spinal cord and its blood supply. Correction of severe scoliosis with Harrington rod instrumentation and spinal fusion is sometimes followed by disastrous neurologic complications: paralysis in both legs, loss of bowel and bladder function. We now use SCEPs, the brain's electrical responses to stimulation of peripheral nerves, to monitor spinal cord function during spinal cord surgery and during neurosurgical procedures on the spine and spinal cord. Anesthetic agents, though they are very necessary, alter SCEPs in ways that must be differentiated from changes due to surgical manipulation. We hypothesized that several anesthetic drugs affect SCEPs in characteristic and dose related ways and that we will be able to identify some agents as effecting SCEPs more than others. We will measure the effects of thirteen drugs commonly used during anesthesia on amplitudes and latency of SCEP peaks, determining the dose response relationship for ten of these agents. Ninety patients will be studied during anesthesia and operation, using a Nicolet MED 80 system for monitoring SCEPs and Hewlett Packard physiologic monitoring equipment to document steady state conditions during SCEP measurements. Definition of anesthetic effects on SCEPs is important for three reasons: 1. It will improve the reliability of SCEP monitoring as an index of spinal cord function during anesthesia and surgery; 2. It will facilitate the development of SCEP monitoring for assessment of brain function during anesthesia; 3. It will shed light on the neurophysiologic aspects of anesthetic action.